Turbine blade



Patented Dec. 20, 1938 Union Carbide and Carbon Research Laboratories, Inc., a corporation of New York Serial No. 77,549

No Drawing. Application May 2, 1936,

2 Claims.

This invention relates to improved high-chromium alloy steel turbine blades for use at elevated temperatures.

It isimportant that the blades employed in tur- 5 bines possess high strength and appreciable ductility and toughness when exposed to superheated steam at high pressures. In addition to these special engineering characteristics the steel must retain satisfactory strength and ductility for a reasonable length of time at the operating temperature, and must offer considerable resistance rosion, without decreasing undesirably the ductility of the material.

The effect of nitrogen in increasing the hardenability of the high chromium steels without seriously decreasing their ductility or toughness is clearly illustrated by the following table of data representing the physical properties of several steels containing about 13% chromium, about 0.07% carbon, small fractional amounts of silicon and manganese; and the amounts of nitrogen indicated in the first column:

Condi- Percent Maximum Percent Izod Percent tion of Yield pt Stresq elonga- Red of 1m Brinell pact 15 N metal lb./sq 1n Ill/Sq m tiozn m area it. L hardness 0.025 1 139,000 151,000 l l 5 293 0 025 2 66, 000 95, 500 23 60 58 187 0 025 3 44, 000 78, 500 30 71 101 137 0. 08 1 178, 000 194, 000 6 11 4 402 0.08 2 106, 500 123, 500 21 65 60 22s 0. 08 3 6B, 500 90, 500 26 60 100 I 179 l-Oil quenched from 950 0.

2-0il quenched from 950 0., then held 2 hours at 600 C. and air cooled. v 3 ==He1d 3 hours at 750 C. and air cooled. 4 25 to the oxidation that normally occurs at elevated temperatures;

In the early attempts to employ high chromium steels for this purpose, it was found that the chromium content must be closely controlled if the desired physical characteristics were to be attained. If the chromium content is too low. the strength of the steel is too low and the steel does not offer sufficient resistance to oxidation. 5 On the other hand, if the chromium is too high, thesteel cannot be given satisfactorily high strength, without at the same time rendering it excessively brittle. Thus, it was found necessary-to employ a steel containing between about 40 11% andabout 14% chromium. Even in steels of this type difliculty has been met in securing the desired strength without producing an undesirable brittleness. Some improvement has been secured by introducing small amounts of certain 4 hardening elements, such as nickel, copper, tung-= sten, and molybdenum.

I have found that certain chromium steels containing nitrogen perform unusually well as turbine blades. Although the usefulness of this 50 discovery is not limited to or by any theory, it is believed that the presence of chromium nitrides, which have a high solubility in the chromium iron solid solutions, greatly increases the hardening capacity of the steels, and it imparts im- 55 proved hardenability without rendering the metal excessively brittle or of inferior ductility. Furthermore, when nitrogen is present in the steels, it is possible to increase the chromium content and thereby secure a-greater resistance to cor- According to the present invention turbine blades comprise steels having a chromium content between about 12% and 16%, carbon in amounts up to about 0.20%, about 0.05% to 0.20% nitrogen, and the remainder iron, except for the customary small amounts of impurities and alloyed additions made to ordinary steels of'similar chromium content. Preferably, .neither the nitrogen content nor the carbon content exceeds about 0.12% of the steel.

I claim:

1. Turbine blade having high strength, high resistance to oxidation -and high ductility and toughness when exposed to superheated steam at high pressures, said turbine bladebeing composed of a steel containing about 12% to about 16% chromium, carbon in amounts up to about 0.2%, and about 0.05 to less than 0.2% nitrogen, the remainder' being substantially all iron, the nitrogen being distributed substantially uniformly throughout the steel.

2. Turbine blade for use athigh temperatures and having high strength, high resistance to oxidation, and high ductility and toughness when the steel.

. RUSSELL FRANKS. 

